Kansas was one of four states that went to the polls Tuesday — the others were Michigan, Missouri and Washington — but the challenge to Roberts, a Washington fixture for decades, took center stage.

A former congressional staffer who served eight terms in the House before winning election to the Senate in 1996, Roberts faced a combative challenge from Wolf, who painted the three-term senator as the personification of the Washington establishment.

A distant cousin of President Obama, Wolf called himself "a doctor, not a politician," and donned a white lab coat in ads. He fashioned himself as a Kansas version of Texas GOP Sen. Ted Cruz and hoped to rally Tea Party energy behind his campaign.

Wolf's effort got a boost in February after a New York Timesstory chronicling the details of the senator's residential situation exposed the 78-year-old Roberts to criticism that he had lost touch with his home state.

But Wolf was hobbled with his own share of bad press: He was criticized for posting X-ray photos of patients' injuries on Facebook and for making comments mocking gunshot victims.

In the state's Wichita-based 4th Congressional District, GOP Rep. Mike Pompeo fended off a challenge from former Republican Rep. Todd Tiahrt, who sought to win back the seat he vacated in 2010 to run for Senate.

In Michigan, however, GOP Rep. Kerry Bentivolio was defeated, making him the third House member to lose in a primary this year. Bentivolio was often referred to as the "accidental congressman," who, as a Tea Party challenger in 2012, was swept into office after Rep. Thaddeus McCotter unexpectedly failed to make the ballot in the suburban Detroit-based 11th Congressional District.

Bentivolio's opponent, real estate attorney David Trott, outspent the freshman congressman by a wide margin — he sunk more than $3.5 million of his own money on the campaign; the incumbent raised $570,000 — while Bentivolio barely even campaigned. The results reflected it: Trott defeated him 66 percent to 34 percent, a stunningly large losing margin for an incumbent.

Elsewhere in the state, in the Grand Rapids-based 3rd Congressional District, Rep. Justin Amash, a libertarian-minded Republican at odds with the GOP establishment, weathered a strong challenge from businessman Brian Ellis. Ellis was backed by the Chamber of Commerce and loaned himself more than $1 million, but Amash managed to hold him off, 57 percent to 43 percent.

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